Rotary/nutating drive

ABSTRACT

A nutating drive comprising a housing with a rotor mounted for axial rotation in the housing and an elongated nutating bar retained at one end thereof in a rotary bearing which is connected to the rotor via a drive coupling at a position offset from the rotor axis for imparting nutational movement to the bar about a geometric center of nutation with axial rotation of the rotor. The drive coupling which connects the nutating bar bearing to the rotor is comprised of a flexible sheet support having outer edges secured to the rotor which permits limited pivotal movement of the bar bearing relative to the rotor. This flexible sheet support may be provided in the form of a single flexible disk or as multiple flexible support strips. In either case, support is provided with at least one undulation extending in the radial direction to enhance pivotal flexibility.

CROSS REFERENCE

[0001] This application is a continuation in part of application Ser. No. 10/051,858, filed Jan. 22, 2002, for Hermetically Sealed Rotary/Nutating Drive.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a device for transmitting rotary motion through a flexible hermetic seal, requiring no gaskets or sliding seal members. More particularly, it relates to said device wherein particular attention is focused on the configuration and mounting of the flexible seal, with the end in view to reduce the stress levels in the flexible seal as much as possible. As is well known, reducing the stress levels in any flexing component will improve its structural integrity and prolong its useful life. This invention offers the longest fatigue life at the highest speed for devices of its kind.

[0003] This hermetic sealing invention would take the place of a typical mechanical seal (such as a face seal) in any rotary device where it is installed.

[0004] Transmission of rotary motion through a hermetic seal finds many applications. Some of these applications are process control pumps, valves and rotating machinery for environmentally hazardous gases/chemicals, “teaspoon” centrifugal pumps for assisting blood circulation and cardiopulmonary bypass, mechanisms for control in contamination-free environments, such as the semi-conductor industry, and aircraft instruments.

[0005] There are many inventions that can address the above applications, and all of them require some form of flexible seal. However, the seals in all of these inventions are far more stressed than they need to be. My invention has minimization of stresses in the flexible seal as one of its primary objects.

[0006] Specifically, my invention belongs to the class of those prior devices where two rotational elements that consist of input and output are rotatably journalled in opposite walls of a housing, and rotary motion between the input and output is transmitted by means of a rigid arm, that can nutate about a central point located between the ends of the arm. The opposite ends of the nutating arm move in circular paths, according to the rotation of the input and output elements. A flexible seal of one sort or another hermetically seals off the rotational elements from each other. The most successful flexible hermetic seal is a bellows, where one end of the bellows is attached to the housing, while the other end of the bellows is attached to the nutating arm. My invention embodies specific improvements on the said prior art. These said improvements, along with other improvements, are discussed below.

OBJECTS AND FEATURES OF THE INVENTION

[0007] An object of the present invention is to provide a unit for hermetic sealing between two in-line rotary devices, each of which device already independently exists. In this sense, the invention is like a kit. In the prior art, because the in-line rotary devices to be hermetically sealed are not pre-existing, these said rotary devices are accordingly newly designed, along with the various invented drives. In my invention, the new drive can be readily adapted as a kit, to fit any two already existing in-line rotary devices without altering these various devices or changing any of the loading they would experience in their normal operation. Thus, my invention can be used as a kit with already existing pairs of rotary devices, while the prior art cannot be so used.

[0008] Another object of the present invention is to supplant mechanical seals wherever possible. Mechanical seals leak, since they cannot be sealed hermetically.

[0009] Another object of the present invention is to avoid high torsion stress in the bellows or tubular diaphragm seal. None of the prior devices has satisfactory provision to avoid said torsion stress. A further object of the present invention is to minimize bending stress in the bellows. In prior devices, that end of the bellows that is attached to the moving arm is attached too far from the center of nutation, so that said end of the bellows travels excessively. The result is, that at high speeds, dynamic bending stresses in the bellows can get large. Also, the prior devices are stressed higher in static bending than they should be. Said prior devices do not make full use of some of the design possibilities that are available for reducing static and dynamic bending stress.

[0010] Yet another object of the present invention is to reduce over-constraint when it is assembled, so that any extra and unnecessary stresses due to misalignment will be minimized in the bearings, balls, bearing supports, swivel joint and arm. Those prior devices that have rotors at both the input and output ends can be over-constrained unless the alignment is very accurate.

[0011] The rotating drive of the present invention is comprised of a housing with an axially rotor mounted for axial rotation in the housing and an elongated nutating bar is retained at one end thereof in a rotary bearing which is in turn connected to the rotor via a drive coupling in a position which is offset from the rotor axis for imparting nutational movement to the bar about a geometric center of nutation with axial rotation of the rotor. The drive coupling is comprised of a flexible sheet support having outer edges secured to the rotor and which permits limited pivotal movement of the bar bearing relative to the rotor. In one embodiment, this flexible sheet support is comprised of a flexible disk having at least one annular undulation concentric with the bearing. In another embodiment, the sheet support is comprised of multiple flexible support strips that extend radially from and are annularly spaced uniformly about the bar bearing. The support strips have at least one undulation in the radial direction for assisting and permitting limited pivotal flexing of the bearing.

[0012] In order to cause a minimal flexing of the flexible sheet support, it is desirable that the support sheet be supported in a plane perpendicular to the nutating bar.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

[0013]FIG. 1 shows my invention installed between two already existing rotary devices.

[0014]FIG. 2 is an elevation view of my invention, and

[0015]FIG. 3 shows its plan view.

[0016]FIG. 4 shows the special wind-up torsion tube used in my invention.

[0017]FIG. 5 is an elevation view of another embodiment, where, instead of an output rotor, there is a paddle for rotating a fluid, as with a “teaspoon” centrifugal pump.

[0018]FIG. 6 is a plan view of FIG. 5.

[0019]FIG. 7 is an elevation view of yet another embodiment, where, instead of using ball and socket arrangements to act as pivots, flexible supports are used.

[0020]FIG. 8 is a half section end view of FIG. 7.

[0021]FIG. 9 is a partial view in side elevation illustrating another embodiment of the flexible supports utilized in the nutating drive of the present invention as shown partially in mid section.

[0022]FIG. 10 is a half section end view of the structure shown in FIG. 9.

BRIEF DESCRIPTION OF THE INVENTION AS TYPICALLY APPLIED

[0023]FIG. 1 shows the invented drive 1 secured to a stand 2, between two already existing rotary devices 3 and 4. Items 2,3, and 4 are mounted on a base plate 5. Also shown is a chamber 6, with a thru-hole 7 in wall 40, which chamber is also mounted on the base plate 5. A boot 8 is affixed seal-tight on either end, to the chamber 6 and to the invention 1. The chamber 6, the boot 8, and the invention 1 contain a fluid or a gas 9, and prevent its escaping to the ambient 10. Also shown are driving/driven shaft 11, of the already existing rotary device 3, said shaft 11 being inserted into the invention 1, and driving/driven shaft 12, of the already existing rotary device 4, said shaft 12 also being inserted into the invention 1. The invented drive 1 allows rotary device 3 to drive rotary device 4 (or visa-versa) while hermetically sealing off rotary device 3 from the ambient.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0024] 1.0 First Preferred Embodiment (See FIGS. 1 through 4)

[0025] (a) The Components of the Drive

[0026] Components of the invented drive are shown in FIGS. 2 and 3. The components are as follows: a cylindrical hole 13 with a keyway 14 is located on the axis of a rotor 15. These items 13, 14 and 15 can accommodate a rotating shaft 11 coming from rotary device 3. (Shaft 11 is not a component of the invented drive unit). The rotor 15 is mounted on bearings 16, and these bearings are mounted on the housing 100. Included is a ball 17, which is free to rotate within a spherical cavity 18 located in the rotor 15. Mounted within the ball 17, and supported by the bearings 71 is an arm 19. Arm 19 is stepped up to a section 20 of larger diameter, and this larger diameter section 20 of the arm is tightly fitted into a yoke 21. Yoke 21 has extensions 22 to accommodate trunnions 23 and 24 (See FIG. 3), which are attached to a gimbal 25. Gimbal 25 has two other trunnions attached to it. One trunnion 72 is attached to the top of the gimbal 25 and the other trunnion 27 at the gimbal's bottom (See FIG. 2). The trunnions 72 and 27 are journalled into the housing 100. The items 21, 22, 23, 24, 25, 72 and 27, as supported by the housing 100, constitute a swivel universal joint; in which the azimuth axis passes through the trunnions 72 and 27, and in which the elevation axis passes through the trunions 23 and 24. A geometric center 50 of nutation exists where the azimuth and elevation axes intersect. Section 20 of the arm is mounted on bearing 25, and bearing 25 is mounted in a ball 26. Ball 26 resides in a spherical cavity 27 located in the rotor 28, and rotor 28 is mounted on bearings 29, which are in turn mounted on the housing 100. A cylindrical hole 30 with a keyway 31 is located on the axis of rotor 28. These items 30,31 and 28 can accommodate shaft 12 of the already existing rotary device 4. (Shaft 12 is not a component of the invented drive unit). Rotor 28 is the output rotor of the drive. The axes of rotors 15 and 28 are ideally collinear. A tapered bellows 32 is attached seal-tight to a housing wall 33 at the largest bellows diameter, and also attached seal-tight to one end 34 of a wind-up torsion tube 35 at the smallest bellows diameter, said smallest bellows diameter and said end 34 of the wind-up torsion tube being located slightly beyond the geometric center 50, where the arm 19 travel is zero. The wind-up tube 35 is attached at its other end 36 to the arm 19. There is a very small clearance 37 (See FIG. 4) between the wind-up tube 35 and the arm 19. This clearance allows the wind-up tube to bend somewhat with respect to the arm 19. Attached seal-tight to the outside wall of the housing 100 is a boot 8, with its smaller end 38 attached seal-tight to the housing 100. The other end 39 of the boot 8 is attached seal-tight to the wall 40 of the chamber 6, which contains rotary device 3.

[0027] (b) The Drive's Hermetic Sealing Boundary

[0028] The hermetic sealing boundary exists by virtue of the wall 40, the boot 8, the housing wall 33, the tapered bellows 32, the wind-up tube 35, and the arm 19.

[0029] (c) Operation of the Drive

[0030] The boot 8, while serving as part of the sealing boundary 40,8,33,32,35, & 19, also serves to keep the housing 100 from rotating around its longitudinal axis during operation of the drive.

[0031] As an example of the operation of the drive, assume that the rotary device 3 is driving the rotary device 4. Then, shaft 11 turns rotor 15 via the round shaft hole 13 with the keyway 14. Turning the rotor 15 rotates the ball 17, and also moves said ball 17 in a circular path around the axis of said rotor 15. (The ball 17 rotates along with the rotor 15 that encases it, because there is some frictional resistance between the ball 17 and the spherical cavity 18 in which it resides). Moving ball 17 along a circular path forces the end of the arm 19 to follow the same circular path as the ball 17. The purpose of bearing 71 is to isolate the arm 19 from rotation of the ball 17, as it moves along its circular path. By virtue of the swivel universal joint arrangement (21, 22, 23, 24, 25, 72 and 27), the arm 19 is allowed to nutate, but it is restrained from rotation. This is the reason why the arm 19 has to be isolated against the rotation of ball 17 by the bearing 71. The arm 19 nutates about the geometric center 50 of nutation of the swivel joint (21, 22, 23, 24, 25, 72 and 27), which geometric center 50 is a virtual pivot point for the nutation of the arm 19. The arm section 20 of larger diameter nutates along with the arm 19 about the same virtual pivot point 50. The purpose of the bearing 25 is similar to that of bearing 71. It isolates the arm section 20 from the rotating ball 26 as it follows its circular path around the axis of rotor 28. Rotor 28 is free to rotate about bearings 29. A torque can be exerted about the axis of the rotor 28 by virtue of the force that can be transmitted by the end of the nutating arm section 20 via the bearing 25, the ball 26, and the cavity 27 within the rotor. The torque will exist when the shaft 12 to be driven by the rotor 28 resists rotation of the said rotor 28 via the hole 30 and the keyway 31. A resisting torque is to be expected because the rotary device 4 is being driven, in this example, by rotary device 3 via the invented drive 1. Because of this resisting torque, various other loads will exist within the invented drive 1. These are the force at the larger diameter end of the arm 20, the force at the small diameter end of the arm 19, and the net counteracting force at the universal swivel joint. The net counteracting universal swivel joint force statically balances the force at the end of the arm 19 and the force at the end of its larger diameter section 20. A force equal and opposite to the said universal swivel joint force is supplied by the housing 100, and this force is in turn transmitted from the housing 100 to the supporting lugs 44. Other loads existing within the housing 100 are torques acting about the azimuth and elevation axes of the housing. These torques are generated by the forces at the ends of arm 19 and the larger diameter section 20, because these said forces are located off-center from the drive's axis of rotation. During operation of the invented drive 1, the supporting lugs 44 resist rotations of the housing 100 in azimuth and elevation. Housing 100 rotation about its longitudinal axis is also prevented by these lugs 44 with the help of the boot seal 8. The shallow groove 45 provides extra clearance, so that the yoke 21 does not touch the housing 100 as said yoke oscillates back and forth during operation of the drive.

[0032] The travel and the amount of bending at the moving end of my tapered bellows 32 are both kept small, because this moving end is extended only slightly beyond the arm's virtual pivot point (fulcrum), where the motion of the arm 19 is minimal. Said smaller end of the tapered bellows 32 is welded to one end 34 of a long and thin wind-up or torsion tube 35 (See FIGS. 3 and 4), whose end 34 also extends slightly beyond the arm's pivot point, and whose other end 36 extends back to the end of the arm 19 where it is attached seal-tight. Minimizing the travel at the moving end of the bellows has the effect of reducing the movement of the other parts of the bellows as well, and this, (along with having the bellows diameter smaller near the fulcrum), contributes to minimizing the static and dynamic bending stresses in the bellows' wall.

[0033] The long and narrow wind-up tube 35 protects the bellows 32 from the torsion stresses that it would otherwise experience when and if the nutating arm 19 should rotate. (Arm 19 could rotate if the bearings 71 or 25 show any tendency not to turn easily). When this happens, the rotation of the rotor 15 or the rotor 28 tends to rotate the arm 19. Slight rotations of the nutating arm 19 are allowed by the swivel joint, because the swivel joint has to have some play in it. Most of that play would come from the trunnions 23, 24, 72, and 27, and, until the trunnions use up their clearance in the holes in which they are journalled, the universal swivel joint will not stop rotation of the arm 19. Therefore, any torsion coming from either bearing 71 or bearing 25, would rotate the arm 19 about its longitudinal axis until the universal swivel joint stops it. Said torsion coming from the bearings (71 or 25), could be the result of the friction caused by normal operation, dirt, wear, and fatigue failure of a bearing. Because of the swivel joint and the long and narrow wind-up tube 35, the torsion on the bellows is never permitted to get large. If arm 19 should experience some rotation as a result of a sticky bearing (71 or 25), where said rotation is not yet opposed by the swivel joint, the long and skinny wind-up tube 35 will take up that rotation and thereby protect the bellows until the swivel universal joint stops any further rotation of the arm 19. The swivel universal joint will be designed for minimum play and maximum structural rigidity. Combined with the high flexibility of the wind-up tube 35, these aforesaid swivel joint characteristics will assure that the torsion stresses in both the wind-up tube and the bellows 32 will be negligible for all possible scenarios.

[0034] (d) Adaptability

[0035] The boot 8 allows my invention to hermetically seal off one already existing rotary device 3. A thru-hole 7 in the wall 40 (see FIG. 1), as well as hole 13 and keyway 14 can accommodate shaft 11 from said rotary device 3. Hole 30 and keyway 31 can accommodate shaft 12 from the other already existing rotary device 4. Lugs 44 attached to the stand 2 (see FIG. 1) resist azimuth and elevation torques coming from the housing 100. These torques are generated by the moving components inside the housing 100. The lugs protect the shafts 11 and 12 and their supporting bearings (which are inside the already existing rotary devices 3 and 4) from the forces caused by said azimuth and elevation torques. Instead of the bearings within the device 3 and 4, the bearings 16 and 29 of the invented device 1 will support the said forces caused by the said torques. Various rotors 15 and 28 of the same diameter can be provided with different standard sizes for the holes 13 and 30, along with different standard keyways 14 and 31, so that the invention unit can be readily applied as a kit to various pairs of already existing devices. Because of the invented device 1, the rotary device 3 does not require a mechanical seal.

[0036] 2.0 Second Preferred Embodiment (See FIGS. 5 and 6)

[0037] The second embodiment of my invention is an improved version over the prior art of the so-called “teaspoon” centrifugal pumps. Prior art “teaspoon” centrifugal pumps have an unusual impeller, which impeller consists of a paddle mounted on the end of a nutating arm. The paddle spins the fluid around like a teaspoon in a teacup. With said form of impeller; the use of bearings immersed in the pumped fluid is avoided. (Bearings that are immersed in some fluids, such as blood, damage the fluid). Said prior art “teaspoon pumps” all have flexible seals of one sort or another, to hermetically seal off the nutating arm. Unfortunately, the seal designs are over stressed from the standpoint of achieving a long fatigue life, and the reliability that goes hand in hand with it. The need for reliability in such devices should be particularly urgent when said devices are used for medical purposes.

[0038] The second embodiment of my invention is an improvement over the prior art of “teaspoon” pumps, because my design drastically reduces the torsion and bending stresses in the flexible seal.

[0039] To obtain all the improvements achieved by the first embodiment, the second embodiment of my invention is constructed identically to the first embodiment, except for three changes: The first change is that a paddle 301 replaces ball 17, bearing 71, rotor 15, and bearings 16. (See FIGS. 2, 3, 5, and 6.) The second change is that flanges 401 and 402 are introduced. The third change is that arm 19 is now inserted into a slot 501, which has been bored into the larger diameter section 20 (See FIG. 5).

[0040] The paddle 301 circulates the fluid 9 to create the vortex necessary for centrifugal-type pumping.

[0041] The flanges 401 and 402, and the slot 501 allow the entire assembly of the swivel joint, the yoke 21, the larger diameter section 20, the ball 26, the bearing 25, the rotor 28, the bearings 29, and the housing 602 to be replaced, if said assembly should wear out. To remove/replace the aforesaid assembly, it is only necessary to bolt/unbolt the flanges 401 and 402, and slide the larger diameter section 20 off/on the arm 19 via the slot 501. Remaining unchanged, and attached to the wall 40 by the boot 8 are the left hand side of the housing 601, the arm 19, the wind-up tube 35, the bellows 32, and the paddle 301.

[0042] Because of its inertia, the fluid circulated by the paddle 301 would necessarily exert a strong torque on the arm 19, and the wind-up tube 35 protects the bellows 32 in the same way here as for the first embodiment.

[0043] 3.0 Third Preferred Embodiment (See FIGS. 7, 8, 9 and 10).

[0044] The first example of the third embodiment of my invention (see FIGS. 7 and 8) is similar to the first and second embodiments, except that instead of using the ball and socket arrangement to act as a pivot, it uses a specially designed flexible support arrangement for the same purpose. This anisotropic flexible pivot support arrangement is less expensive to manufacture than the ball and socket arrangement.

[0045] The anisotropic flexibility support arrangement is designed to be very stiff in the driving direction (tangential to a circle of rotation about the common axis of the rotors), but somewhat flexible in the other two orthogonal directions. This support arrangement is also flexible in rotation about two of the three aforementioned orthogonal directions. These various limited flexibilities are needed to provide a pivot that avoids over constraining the bearings, the swivel joint, and the nutating rod, while still driving the rotor.

[0046] In this embodiment, this flexible sheet support is made up of the brackets 701, the flexible support strips 702, and the bearing housing 703, and replaces the ball (17 or 26) and the cavity (18 or 27) of the previous embodiments. Two brackets 701 are attached to each rotor (15 or 28). Two flexible support strips 702 are attached to the brackets 701 and to each bearing housing 703. The flexible strips 702 has a convoluted section 704 and a straight section 705 thereby providing at least one undulation in the radial direction. The convoluted section 704 provides flexibility in the axial and radial directions, as well as rotational flexibility about a radial axis running perpendicular to the flexible strips 702. The straight section 705 provides rotational flexibility about a radial axis that runs through the flexible 702.

[0047] A hole with a spline 706 in it is preferred to the keyway 14 arrangement of the previous embodiments. Also, in the interest of saving cost, a short non-tapered bellows 801 is preferred in this embodiment over the tapered bellows 32 of the previous two embodiments.

[0048] The embodiment shown in FIGS. 9 and 10 illustrate a variation in structure for the flexible sheet support 702. In this embodiment, the flexible sheet support 702 is comprised of a single flexible disk as opposed to multiple support strips. The flexible disk 702 (flexible sheet support) is provided with at least one annular undulation as indicated at 704 which is concentric with bearing 703. This provides the requisite limited pivotal movement as previously explained with regard to the configuration illustrated in FIGS. 7 and 8.

[0049] Another variation illustrated in FIGS. 9 and 10, as opposed to the structure shown in FIGS. 7 and 8, is that the support bracket 701 in FIG. 7 and 8 which supports the flexible sheet support 702, is segmented and supports the flexible sheet support 702 in parallel to the inside base of rotor 15. However, in the structure of FIGS. 9 and 10, the bearing 71 and the flexible disk providing flexible sheet support 702 are instead supported in a plane perpendicular to bar 19, instead of in parallel with the interface of rotor 15. Here the support bracket 701 is annular. This arrangement provides minimal flexing of flexible sheet support 702 thereby providing the longest possible life. 

I claim:
 1. A nutating drive comprising: a housing; an axially rotatable rotor mounted for axial rotation in said housing; an elongated nutating bar retained at one end thereof in a rotary bearing which is connected to said rotor via a drive coupling at a position offset from the rotor axis for imparting nutational movement to said bar about a geometric center of nutation with axial rotation of said rotor; said drive coupling comprised of a flexible sheet support having outer edges secured to said rotor and which permits limited pivotal movement of said bar bearing relative to said rotor.
 2. The nutating drive of claim 1, wherein said flexible sheet support is comprised of a flexible disk having at least one annular undulation concentric with said bearing.
 3. The nutating drive of claim 1, wherein said flexible sheet support is comprised of multiple flexible support strips extending radially from and annularly spaced uniformly about said bar bearing, said support strips having at least one undulation in the radial direction.
 4. The nutating drive of claim 1, wherein said flexible sheet support is supported in a plane perpendicular to said bar. 